You are incorrect in your statement about MRSA. For staph aureus
most of the resistance mechanisms are due to plasmid transmission
of already existing genes, or tranposons, or mutation of
a gene alreay present. There may be two "novel" chromosomal
areas which have been acquired from an unknown source. Most
of the resistance is therefore due to already existing genes.
At least two are of unknown origin.
"A new b-lactam-inducible penicillin-binding protein (PBP) that has extremely low affinity to penicillin and most other b-lactam antibiotics has been widely found in highly, b-lactam(methicillin)-resistant Staphylococcus aureus (MRSA). The gene for this protein was sequenced and the nucleotide sequence in its promoter and close upstream area was found to show close similarity with that of staphylococcal penicillinase, while the amino acid sequence over a wide range of the molecule was found to be similar to those of two PBPs of Escherichia coli, the shape-determining protein (PBP 2) and septum-forming one (PBP 3). Probably the MRSA PBP (Mr 76462) evolved by recombination of two genes: an inducible type I penicillinase gene and a PBP gene of a bacterium, causing the formation of a b-lactam-inducible MRSA PBP."
"Evolution of an inducible penicillin-target protein in methicillin-resistant Staphylococcus aureus by gene fusion." Song, M.; Wachi, M.; Doi, M.; Ishino, F.; Matsuhashi, M. FEBS Letters, 1987, 221, 167-171.
Maybe if you write them a letter they'll issue a correction even at this late date.